Pre-Treatment Method for Plating and Instrument for Waterworks of Lead-Contained Copper Alloy

ABSTRACT

A pre-treatment method for plating wherein lead or the like dissolved in an etching liquid is not electro-deposited (re-adhesion) on a lead-contained copper alloy to be plated even without adding a chelating agent forming an insoluble inert combined substance. The lead-contained copper alloy to be plated is dipped in an alkaline etching liquid without adding a chelating agent which would form an insoluble inert combined substance. In this state, electrolysis where the lead-contained copper alloy functions as one of a positive electrode and a negative electrode, and electrolysis where the lead-contained copper alloy functions as the other of the positive electrode and the negative electrode are performed alternately (PR electrolysis).

TECHNICAL FIELD

The present invention relates to a pre-treatment method for plating of preliminarily removing lead existing on a surface layer of a lead-contained copper alloy prior to carrying out the plating on a surface of the lead-contained copper alloy and to an instrument for waterworks of the lead-contained copper alloy obtained by the application of the pre-treatment method for plating.

BACKGROUND ART

As a material for an instrument for waterworks there is generally used a lead-contained copper alloy which is superior in workability and protection against corrosion. Since this lead-contained copper alloy contains lead harmful to the human health, plating is carried out on a surface of the alloy in a process step as shown in FIG. 3 so as to prevent the lead from being eluted out.

To put it concretely, the lead-contained copper alloy is dipped in an alkaline etching liquid as a pre-treatment to remove the lead from a surface layer of the lead-contained copper alloy. Then, after carrying out nickel plating, chromium plating and chromate treatment, the lead-contained copper alloy is washed.

The above pre-treatment is the treatment for removing stains on the surface so as to facilitate the formation of a plated layer and for preventing the elution of lead. The applicant of the present invention paid attention to a characteristic that lead is amphoteric metal and proposed the method of removing lead by both of alkali and acid by adding an oxidizing agent to the alkaline etching liquid (see patent reference 1).

Further, there is known an alkaline electrolytic cleaning method of removing the stains on the surface by electrolysis while dipping the lead-contained copper alloy in the alkaline etching liquid. As an electrolysis method there are cathode electrolysis that the lead-contained copper alloy functions as a negative electrode and anode electrolysis that the lead-contained copper alloy functions as a positive electrode. In the anode electrolysis, oxygen gas is generated on the surface of the lead-contained copper alloy so as to decompose and remove organic stains on the surface of the lead-contained copper alloy by the gas, so that it is superior in cleaning effect. However, since the lead-contained copper alloy is dissolved by the electrical operation (etching), roughness (over-etching) of a basis material is apt to occur in the lead-contained copper alloy. Therefore, there is also used the cathode electrolysis method that dissolution of the lead-contained copper alloy does not occur and hydrogen gas is generated on the surface of the lead-contained copper alloy. A PR (periodic reverse) electrolysis method that repeats the cathode electrolysis and the anode electrolysis alternately is also known.

In the case where the cathode electrolysis method is selected for the pre-treatment for plating of the lead-contained copper alloy, since the object to be plated (the lead-contained copper alloy) becomes the negative electrode, electro-positively charged ions such as lead (Pb⁺) dissolved in the alkaline etching, heavy metals contained as impurities in the etching liquid, etc. are electro-deposited (the same operation as plating) on and re-adhered to the surface of the plated object by the electrical operation.

This re-adhesion causes adherence failure in the following plating and tarnish after the plating. Therefore, there is proposed a method in which a chelating agent which forms an insoluble inert combined substance is added to the alkaline etching liquid and an insoluble chelating compound is formed by having the lead dissolved in the alkaline etching, etc. reacted on the chelating agent so as to remove the insoluble chelating compound by precipitating it before being electro-deposited on the surface of the plated object (see patent reference 2).

Patent reference 1: Japanese patent No. 3182765.

Patent reference 2: Japanese patent application publication No. H02-274900.

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

In the method of adding the oxidizing agent to the alkaline etching liquid to remove lead as disclosed in patent reference 1, there may be cases degreasing power is not sufficient because of being not dependent on the electrolysis. Also, in a case where a chelating agent forming an insoluble inert combined substance is added to the alkaline etching liquid when carrying out the cathode electrolytic cleaning in the state that the lead-contained copper alloy is dipped in the alkaline etching liquid as disclosed in patent reference 2, the electro-deposition (re-adhesion) can be prevented but the degreasing power may be insufficient merely by the application of the cathode electrolysis. Further, the addition of the chelating agent incurs an increase in costs for that.

Means for Solving the Problem

To solve the above mentioned problem, a pre-treatment method for plating, according to the present invention, of preliminarily removing lead existing on a surface layer of a lead-contained copper alloy prior to carrying out nickel plating or chromium plating on a surface of the lead-contained copper alloy, comprising the step of performing electrolysis where the lead-contained copper alloy functions as one of a positive electrode and a negative electrode, and electrolysis where the lead-contained copper alloy functions as the other of the positive electrode and the negative electrode alternately (PR electrolysis) in a state where the lead-contained copper alloy is dipped in an alkaline etching liquid.

In the PR electrolysis it is preferable that the lead-contained copper alloy functions as a positive electrode at the end. Also, as conditions of the PR electrolysis it is preferable that electric current density is 1 A/dm² or more and 25 A/dm² or less and a current reversing period is 2 seconds or more and 30 seconds or less. Further, it is also preferable that an oxidizing agent is added to the alkaline etching liquid.

Also, an instrument for waterworks of lead-contained copper alloy, according to the present invention, a surface of which is plated, wherein as pre-treatment for plating, treatment of alternately carrying out electrolysis that the lead-contained copper alloy functions as one of a positive electrode and a negative electrode and electrolysis that the lead-contained copper alloy functions as the other of the positive electrode and the negative electrode is performed in such a state that the lead-contained copper alloy is dipped in an alkaline etching liquid.

In the PR electrolysis being performed when obtaining the instrument for waterworks of the lead-contained copper alloy, it is preferable that lastly the lead-contained copper alloy is the positive electrode in the same way as above. Also, as conditions of the PR electrolysis it is preferable that electric current density is 1 A/dm² or more and 25 A/dm² or less and a current reversing period is 2 seconds or more and 30 seconds or less. Further, it is also preferable that an oxidizing agent is added to the alkaline etching liquid.

EFFECTS OF THE INVENTION

According to the pre-treatment method for plating of the present invention, lead or the like dissolved in the etching liquid is not electro-deposited on or re-adhered to the lead-contained copper alloy to be plated and the degreasing cleaning is sufficiently carried out, so that defects such as tarnish or the like are not caused on the surface after plating. Moreover, no chelating agent which forms an insoluble inert combined substance is used whereby costs can be efficiently decreased.

Further, in the last electrolysis of the PR electrolysis the lead-contained copper alloy to be plated is the positive electrode, so that it is possible to effectively prevent the electro-deposition (re-adhesion) of lead or the like on the surface of the plated object. Furthermore, when the oxidizing agent is added to the alkaline etching liquid in the case of carrying out the PR electrolysis, lead can be removed well due to a characteristic that the lead is the amphoteric metal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart of plating to which pre-treatment for plating of the present invention is applied;

FIG. 2 is a schematic view of PR electrolysis; and

FIG. 3 is an explanatory view showing a conventional plating process.

MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will now be explained with reference to the accompanying drawings. FIG. 1 is a flow chart of plating to which pre-treatment for plating of the present invention is applied, and FIG. 2 is a schematic view of PR electrolysis. In the present invention, when ultra-sonic cleaning and alkaline cleaning is carried out as pre-treatment for plating, PR electrolysis is simultaneously carried out so as to accurately remove stains on a surface of an object (a lead-contained alloy) to be plated. Herein, the ultra-sonic cleaning is not necessarily required, but the application of the PR electrolysis only using the alkaline cleaning liquid may be enough. Meanwhile, following the PR electrolysis using the alkaline cleaning liquid, cathode electrolysis and anode electrolysis may be used solely or in combination as the need arises. Then, the surface of the object (the lead-contained alloy) to be plated is further cleaned thereby to increase adhesiveness of the plating.

A concrete experiment is performed on the plating adhesiveness and the quality of an external appearance by the PR electrolysis without adding a chelating agent which forms an insoluble inert combined substance. Conditions and results of the experiment will be described hereunder. Herein, the object to be plated is a single water faucet of bronze casting.

(Electrolytic Degreasing Conditions, Conditions of Electrolytic Liquid) Alkaline Etching Liquid (Alkaline Cleaning) (1) Main Component:

A plating process generally comprises a degreasing step and a plating step. The degreasing step is the one for removing stains such as oil components, etc. adhered to a base material. The main components of alkaline etching liquid used in the present invention are sodium hydroxide, potassium hydroxide, sodium carbonate, sodium phosphate, sodium tripolyphosphate, sodium meta-silicate, sodium ortho-silicate and the like, and when processing, an alkaline solution in which one or more kinds of these components are dissolved is used. The concentration is generally from several g/L to several 10 g/L. It is to be judged properly by the combination of the components to be used.

(2) Surface Active Agent:

The surface active agent is added with a view to decreasing surface tension of the liquid so as to improve penetration and wettability of the alkaline etching liquid. As the surface active agent, an anionic surface active agent or a nonionic surface active agent is mostly used and each of these surface active agents is used solely or in combination. As the anionic surface active agent there are given higher fatty acid sodium, sulfated oil, higher alcohol sodium ester sulfate, sodium alkyl benzene sulfate, higher alkyl ether sodium ester sulfate and sodium α-olefin sulfate. Further, as the nonionic surface active agent there are given alkyl polyoxyethylene ether, alkyl phenyl polyoxyethylene ether, a fatty acid ethylene oxide addition product and a polypropylene glycol ethylene oxide addition product (pluronic). The addition volume is generally from several g/L to several 10 g/L.

(3) Chelating Agent:

The chelating agent may be added in order for preventing a hydroxide of lead from re-adhesion and at the same time for accelerating the dissolution of lead. As the chelating agent there are preferable such compounds as EDTA, ethylenediamine, triethanolamine, thiourea, Rochelle salt, tartaric acid and the like which are apt to form a complex with lead. It is preferable that the concentration of each component is from several g/L to several 10 g/L.

The chelating agent which forms the insoluble inert product with heavy metal such as lead may be added. As the chelating agent which forms the insoluble inert product, sodium dimethyl dithiocarbamate, sodium diethyl dithiocarbamate and the like are preferable. It is also preferable that the concentration of each component is from several g/L to several 10 g/L.

(4) Oxidizing Agent

In a case of adding the oxidizing agent to the alkaline etching liquid, lead is oxidized and dissolved via lead oxide (PbO, etc.) in alkali, so that the dissolution of lead is accelerated. As the oxidizing agent, there are used organic oxidizing compounds such as sodium methanitro benzene sulfonate, sodium paranitro benzoate and the like, and inorganic compounds such as hypochlorite, bleaching powder, hydrogen peroxide, potassium permanganate, peroxosulfate, perchlorate and the like. It is preferable that the concentration of each component is from several g/L to several 10 g/L.

(Conditions of Plating)

The performed plating is as follows.

(1) Chrome Plating

As a chrome plating bath, a publicly well-known Sargent bath comprised of absolute chromic acid and sulfuric acid can be used. It is also possible to use a chrome fluoride plating bath replacing a part or the whole of sulfuric acid in the Sargent bath with fluoride may be used. When carrying out the chrome plating in the chrome plating liquid, an outer surface is chrome plated while, in an inner surface, lead is dissolved with the dissolution of the entire copper alloy material due to the strong oxidizing property of the chrome plating liquid. In the case of no existence of the fluoride, there is some possibility that a precipitate remains as lead chromate. In this respect, since the fluoride has the function of dissolving the precipitate, it is preferable to carry out the chrome plating in the chrome fluoride plating bath. Then, preferably, the temperature is from 40 degrees centigrade to 60 degrees centigrade and the dipping period is from several 10 seconds to several minutes.

As the fluoride, it is possible to use almost all of fluorine compounds such as sodium fluoride, potassium fluoride, ammon fluoride, hydrofluoric acid, fluoroboric acid, silicofluoric acid, sodium silicofluoride, potassium silicofluoride, chrome fluoroborate and the like.

(2) Chromate Filming

An additive to be used in the chromate filming is based on an absolute chromic acid, a phosphoric acid and a sulfuric acid. As the case may be, it is possible to add or be replaced with a nitric acid, a hydrofluoric acid, an acetic acid, an oxalic acid, chromate and the like. A chromate solution for use in galvanizing, etc on the market may be used.

It is preferable that the concentration of each component is from several g/L to several 10 g/L. Also it is preferable that the temperature for treatment is from an ordinary temperature to 60 degrees centigrade and the period for treatment is from several seconds to several minutes. The product on the outer surface of which the plating is carried out is dipped in the chromate liquid, so that a chromate film is formed in the inner surface thereof so as to prevent the elution of lead. When adding the phosphoric acid to the absolute chromic acid which is a main component of the chromate liquid, the lead elution is more effectively prevented in a synergistic effect.

(Evaluation Test)

After carrying out the above mentioned electrolytic degreasing and the plating (after nickel plating, chrome plating and chromate filming are done in turn), the following evaluation test is performed.

(1) Adhesiveness Test

“21.2 Thermal shock test” of “JIS (Japanese Industrial Standards) H8504 Plating adhesiveness test method” (test method for examining plating adhesiveness by thermal shock of heating and quenching specimen) was performed. As a result, as shown in Table 1 below, there is no problem in adhesiveness other than the cathode electrolysis without a chelating agent which forms an insoluble inert combined substance.

TABLE 1 Cathode Anode PR electrolysis electrolysis electrolysis Without chelating agent NG OK OK With chelating agent OK OK OK

(2) External Appearance Test

“9.2 External appearance test” of “JIS H8617 Nickel plating and nickel-chrome plating” wherein the external appearance test is performed by visual evaluation and whether or not there are plating defects such as roughness, burnt deposits, cracking, pit, exposure of base material, etc., a sign of adhesive failure, a dirty mark, a stain and the like is examined. As a result, as shown in Table 2 below, only the PR electrolysis achieved good results without adding a chelating agent which forms an insoluble inert combined substance.

TABLE 2 Cathode Anode PR electrolysis electrolysis electrolysis Without chelating agent NG NG OK (present invention) With chelating agent OK NG OK

Next, with respect to the anode electrolysis and the PR electrolysis, experiments on the adhesiveness and the external appearance were performed under the following experimental conditions.

First, Table 3 shows experimental results of the anode electrolysis with a chelating agent which forms an insoluble inert combined substance. As the experimental results, the adhesiveness was good in all the experiments, but the external appearance was not good in all the experiments. Herein, as the electrolytic conditions, after ultra-sonic cleaning for one minute by application of ultrasonic waves, the alkaline cleaning was carried out for two minutes.

TABLE 3 Ultrasonic Alkaline External cleaning cleaning Remarks Appearance Anode 1 A/dm² 1 A/dm² Ultrasonic waves NG elec- only 2″ on 2″ off trolysis 0.5 A/dm²   0.5 A/dm²   Ultrasonic waves NG only 2″ on 2″ off 0 A/dm² 1 A/dm² No electrolysis by NG ultrasonic waves 0 A/dm² 5 A/dm² No electrolysis by NG ultrasonic waves

Table 4 shows experimental results of the anode electrolysis without a chelating agent which forms an insoluble inert combined substance. As the experimental results, the adhesiveness was good in all the experiments, but the external appearance was not good in all the experiments. Herein, as the electrolytic conditions, after ultra-sonic cleaning for one minute by application of ultrasonic waves, the alkaline cleaning was carried out for two minutes.

TABLE 4 Pre-treatment conditions Ultrasonic Ultrasonic Alkaline Alkaline External appearance quality cleaning pulse cleaning pulse Gloss Irregularities 0 A/dm² — 1 A/dm² — NG NG 0 A/dm² — 10 A/dm² — NG NG 0 A/dm² — 10 A/dm² 2″ on 2″ off Very bad NG 2.5 A/dm² 1″ on 3″ off 10 A/dm² — NG NG 2.5 A/dm² 1″ on 3″ off 1 A/dm² (80° C.) — NG NG 2.5 A/dm² 1″ on 3″ off 10 A/dm² (80° C.) — NG NG 2.5 A/dm² — 10 A/dm² — NG Very bad 2.5 A/dm² — 2.5 A/dm² — NG Very bad

Table 5 shows experimental results of the PR electrolysis without a chelating agent which forms an insoluble inert combined substance. The adhesiveness and the external appearance were both good in all the experiments. Herein, as the electrolytic conditions, after ultra-sonic cleaning for one minute by application of ultrasonic waves, the alkaline cleaning was carried out for two minutes.

TABLE 5 PR electrolysis (Reversing period: 2″ ⇄ 2″) Quality evaluation (N = 3) Ultrasonic Alkaline External appearance cleaning cleaning Adhesiveness inspection 0 A/dm² 2 A/dm² OK OK 5 A/dm² OK OK 10 A/dm²  OK OK 1 A/dm² 2 A/dm² OK OK 5 A/dm² OK OK 10 A/dm²  OK OK 3 A/dm² 2 A/dm² OK OK 5 A/dm² OK OK 10 A/dm²  OK OK

From the above experiments, it became clear that in the case of application of the PR electrolysis, the adhesiveness and external appearance after plating are good even without adding a chelating agent which forms an insoluble inert combined substance. Therefore, next, experiments on preferable conditions (a reversing period and current density) of the PR electrolysis were performed. In the experiments, the ultra-sonic cleaning was carried out for one minute by application of ultrasonic waves, and thereafter, the alkaline cleaning was carried out for two minutes.

The results are shown in Table 6 below. From Table 6, it becomes clear that a preferable current reversing period is 30 seconds or less and a preferable current density is 25 A/dm² or less.

TABLE 6 Electrode at the end Current Negative Positive Positive Positive Positive Positive Positive reversing electrode electrode electrode electrode electrode electrode electrode period 2″

2″ 5″

5″ 10″

10″ 20″

20″ 30″

30″ 45″

45″ 60″

60″  1 A/dm² OK OK OK OK OK NG NG  3 A/dm² OK OK OK OK OK NG NG  5 A/dm² OK OK OK OK OK NG NG 10 A/dm² OK OK OK OK OK NG NG 20 A/dm² OK OK OK OK OK NG NG 25 A/dm² OK OK OK OK OK NG NG 30 A/dm² NG NG NG NG NG NG NG

From the above, in the case of the PR electrolysis, the plating adhesiveness and the external appearance were ensured even without a chelating agent forming an insoluble inert combined substance. Therefore, next, whether or not the lead elution meets NSF standard and JIS standard was confirmed. A single lever water faucet of bronze casting was used as a sample.

NSF Standard

The concentration of eluted lead was analyzed with respect to the above sample which had undergone a treatment of NSF/ANSI61-2003e “9 Mechanical plumbing devices.”

Standard: 11 ppb or less after conversion

JIS Standard

The concentration of eluted lead was analyzed with respect to the above sample which had undergone a treatment of JIS S3200-7 (2004) “Instruments for waterworks—Leaching performance test method.”

Standard: 7 ppb or less after conversion

Results of experiments are shown Table 7-1 and Table 7-2 below. As apparent from Table 7-1 and Table 7-2, the results of the product obtained by the plating method to which the pre-treatment for plating of the present invention was applied meet NSF standard and the JIS standard.

TABLE 7-1 NSF standard test results Leaching value Correction value NSF 1 13.72 3.16 NSF 2 14.23 3.27 NSF 3 13.68 3.15 Content volume: 230 ml Unit: ppb Correction value = Leaching value x (Content volume/1000)

TABLE 7-2 JIS standard test results Leaching value Correction value JIS 1 16.39 3.77 JIS 2 12.58 2.89 JIS 3 13.07 3.01 Content volume: 230 ml Unit: ppb Correction value = Leaching value x (Content volume/1000) 

1. A plating pre-treatment method for plating of preliminarily removing lead existing on a surface layer of a lead-contained copper alloy prior to carrying out plating on the surface, comprising the steps of: alternately performing electrolysis where said lead-contained copper alloy functions as one of a positive electrode and a negative electrode, and electrolysis where said lead-contained copper alloy functions as the other of the positive electrode and the negative electrode, the steps being performed in a state where said lead-contained copper alloy is dipped in an alkaline etching liquid.
 2. The pre-treatment method for plating according to claim 1, wherein said lead-contained copper alloy functions as the positive electrode in a last-performed one of said electrolysis steps.
 3. The pre-treatment method for plating according to claim 1, wherein the electrolysis steps are performed with conditions of an electric current density of 1 A/dm² r more and 25 A/dm² or less and a current reversing period of 2 seconds or more and 30 seconds or less.
 4. The pre-treatment method for plating according to claim 1, said alkaline etching liquid contains an oxidizing agent.
 5. The pretreatment method for plating according to claim 1, wherein nickel plating is carried out and thereafter chromium plating is carried out as said plating on the surface of the lead-contained copper alloy after said electrolysis steps.
 6. A plating pre-treatment method for a surface of an instrument for waterworks of a lead-contained copper alloy comprising the steps of: alternately performing electrolysis where said lead-contained copper alloy functions as one of a positive electrode and a negative electrode, and electrolysis where said lead-contained copper alloy functions as the other of the positive electrode and the negative electrode, the steps being performed in a state where said lead-contained copper alloy is dipped in an alkaline etching liquid.
 7. The plating pre-treatment method according to claim 6, wherein in the electrolysis performed alternately with the positive electrode and the negative electrode, said lead-contained copper alloy functions as the positive electrode in a last-performed one of the electrolysis steps.
 8. The plating pre-treatment method according to claim 6, wherein the electrolysis steps are performed with conditions of an electric current density of 1 A/dm² or more and 25 A/dm² or less and a current reversing period of 2 seconds or more and 30 seconds or less
 9. The plating pre-treatment method according to claim 6, wherein said alkaline etching liquid contains an oxidizing agent.
 10. The pre-treatment method for plating according to claim 2, wherein the electrolysis steps are performed with conditions of an electric current density of 1 A/dm² or more and 25 A/dm² or less and a current reversing period of 2 seconds or more and 30 seconds or less.
 11. The pre-treatment method for plating according to claim 2, said alkaline etching liquid contains an oxidizing agent.
 12. The pre-treatment method for plating according to claim 2, wherein nickel plating is carried out and thereafter chromium plating is carried out as said plating on the surface of the lead-contained copper alloy after said electrolysis steps.
 13. The plating pre-treatment method according to claim 7, wherein the electrolysis steps are performed with conditions of an electric current density of 1 A/dm² or more and 25 A/dm² or less and a current reversing period of 2 seconds or more and 30 seconds or less
 14. The plating pre-treatment method according to claim 7, wherein said alkaline etching liquid contains an oxidizing agent. 